This invention relates to a method for purifying a chemical mixture containing olefinic impurities, more particularly to purifying a 1,1,1-trifluoro-2-chloroethane ("HCFC-133a" or "133a") product mixture containing olefinic impurities of the formula CF.sub.3 CX.dbd.CYCF.sub.3, where X and Y are independently selected from H, Cl and F. HCFC-133a is used as an intermediate in the manufacture of 1,1,1,2-tetrafluoroethane ("HFC-134a" or "134a"), trifluoroethanol and pharmaceutical products. The aforementioned olefinic impurities have been found to reduce the activity of fluorination catalysts used to convert 133a to 134a. Also, the toxicity of these olefins makes them undesirable impurities in pharmaceuticals. The boiling points of these impurities are close to that of 133a, making them difficult to separate by distillation.
UK Patent Application 2318350 discloses a process to remove olefinic impurities from 133a by photochlorination to produce heavy (high-boiling) compounds. However, the quartz or glass reactors required for such a process are vulnerable to attack by the HF used in a fluorochemicals plant as a fluorinating agent. The photochlorination reaction also produces some 1,1,1-trichloro-2,2-dichloroethane ("123"), which causes a yield loss, and some HCl. A separate method must be used to remove the light (low boiling) impurities (HCl and unreacted chlorine from the photochlorination) and to remove the heavy compounds. Thus, it would be useful to find a simpler, more efficient method for removing olefinic impurities from 133a.